REIMPORT OF EXPORTED GOODS - Customs - Exim - SEZ

Goods exported from India to Canada under RODTEP IGST. Part of the goods returned back within 20 months as goods were defective. Filed for import clearance under notification 045/2017 , serial no. 1A. RODTEP IGST claimed at time of export paid back to customs, as detailed under ntfn 045/17 . Customs is insisting upon payment of interest on RODTEP IGST refunded, although the notification does not ask for interest, only for refund of drawback, RODTEP, IGST claimed at the time of export. Please advise.